Self-Assembly of Novel Functional Nanostructured Materials through Covalent Bond Formation and Their Applications

Abstract

This thesis describes the synthesis and characterization of novel nanostructured materials such as hollow polymer nanospheres and two-dimensional (2D) polymers using rationally designed monomeric units with polymerizable peripheral or meso functional groups through irreversible covalent bond formation. The synthesized materials are utilized for different applications in various areas including therapeutics and electronics. Chapter 1 briefly delineates our recent discoveries in self-assembly of nanostructured materials through strong, irreversible covalent bond formation and their applications. Furthermore, this chapter highlights the potential of this covalent self-assembly approach to generate a diverse range of shape-persistent and robust nanostructures, which is likely to enrich the repertoire of self-assembled nanomaterials. Chapter 2 describes the one-pot direct synthesis of various different hollow polymer nanospheres in template-free manner via covalent self-assembly by utilizing thiol-ene “click” chemistry or olefin metathesis from rationally designed monomers, having rich photophysical and electronic properties, such as subphthalocyanine (SubPc), phthalocyanine (Pc) and anthraquinone (ANTQ) with multiple polymerizable groups at the periphery. The synthesized nanospheres may thus be useful for drug delivery, therapeutics, imaging, and catalysis. Chapter 3 presents the application of subphthalocyanine (SubPc) nanosphere in combating antibiotic resistant bacteria, a major global health threat. The multifunctional SubPc nanosphere has an ability to target, label, and photoinactivate antibiotic-resistant bacteria in a single treatment with more than 99% efficiency. The positively charged nanosphere shell can increase the local concentration of photosensitizers at therapeutic sites and shows superior performance compared to corresponding monomers presumably because of their enhanced water dispersibility, higher efficiency of singlet oxygen generation, and phototoxicity. In addition, this material is used in fluorescence labeling of living cells and shows promise in photoacoustic imaging of bacteria in vivo. Chapter 4 demonstrates the solution phase synthesis of a novel ultrathin 2D polymer (ZnTThP) with large-area and uniform thickness of 2 nm from a π-conjugated porphyrin monomer having four meso-substituted thiophene units via a surface mediated polymerization method. The polymer has been characterized using various spectroscopic and microscopic techniques. Furthermore, the polymer can be easily isolated as free-standing, flexible, large-area ultrathin sheets via a simple etching-induced method. Chapter 5 presents the utilization of ZnTThP polymer for nonvolatile memory application. The device fabricated using ZnTThP polymer shows typical forming-free, bipolar current-voltage (I-V) characteristics and possesses a high ON/OFF current ratio, long retention time, high endurance, and therefore can be a promising alternative material for ultrathin resistive random-access memory (RRAM) applications.